Lens, zoom lens, and imaging lens

ABSTRACT

A lens 1 has unevenness within an optical effective diameter D of an optical surface 2, an arithmetic mean roughness Ra within the optical effective diameter D of the optical surface 2 is 20 nm or more and 50 nm or less, and an average value of widths W of protrusion portions 3 of the unevenness on an average line C2 of a roughness curve C1 of the optical surface 2 is 1/200 or more and 1/50 or less of the optical effective diameter D of the optical surface 2. The lens 1 is suitably used as a lens that composes a zoom lens or an imaging lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of US application No. U.S. Ser. No. 16/547,608 filed on Aug. 22, 2019, now allowed, which claims priority under 35 U.S.C. § 119(a) to PCT International Application No. PCT/JP2018/005873 filed on Feb. 20, 2018, Japanese Patent Application No. 2017-034074 filed on Feb. 24, 2017 and Japanese Patent Application No. 2018-009060 filed on Jan. 23, 2018. Each of the above application(s) is hereby expressly incorporated by reference, in its entirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a lens, a zoom lens comprising the lens, and an imaging lens.

2. Description of the Related Art

For various lenses including television lenses, cine lenses, still lenses, and the like, performances such as reduced size, light weight, high resolution, and high magnification are required, and in addition to those performances, aesthetic quality (smoothness) for blurriness occurred in an image in a defocused state is also required. As blurriness that impairs aesthetic quality of an image, blurriness of a ring zone is present, which appears in a concentric pattern on the image. It is known that the blurriness of the ring zone occurs due to surface unevenness (concentric circle) of a lens used in a lens unit. In the related art, the blurriness of the ring zone is reduced by smoothing a surface of the lens or a surface of a mold used for molding the lens as much as possible (see, for example, Yamagata factory report, “Commitment to manufacturing with high precision lens processing”, [online], CAPA camera net, [searched on Feb. 16, 2017], Internet <URL: http://capacamera.net/gmuseum/special/1301_2.html>, Dave Etchells, “The end of onion-ring bokeh? Panasonic beats the curse of aspheric lenses”, [online], May 2, 2014, IMAGING RESOURCE, [searched on the Feb. 16, 2017], Internet <URL: http://www.imaging-resource.com/news/2014/05/02/the-end-of-onion-ring-bokeh-panasonic-beats-the-curse-of-aspheric-lenses>, and SEL2470GM Features, “A total of three aspheric lenses including newly developed ultra-high aspheric XA (extreme aspherical) lenses are effectively arranged to realize sharp depiction from aperture opening”, [online], Sony Marketing Inc., [searched on Feb. 16, 2017], Internet <URL: http://www.sony.jp/ichigan/products/SEL2470GM/feature_1.html>). Further, each of JP1988-214715A (JP-S63-214715A) and JP1989-147403A (JP-H01-147403A) discloses an optical element for soft focus that has minute unevenness on an optical surface thereof. Although the optical element for soft focus does not have a specific purpose of reduction of the blurriness of the ring zone, the optical element for soft focus is expected to reduce the blurriness of the ring zone.

In a lens disclosed in JP1988-214715A (JP-S63-214715A), a diameter ϕ of a minute light refraction portion (protrusion portion) provided on the optical surface is 0.05 mm≤ϕ≤0.5 mm, a height h from the optical surface to an apex of the minute light refraction portion is 0.5 μm≤h≤3 μm, and a ratio S, in the whole surface area, of the minute light refraction portion to the optical surface is 5%≤S≤35%.

In a lens disclosed in JP1989-147403A (JP-H01-147403A), a surface roughness Rmax of the optical surface is 0.05 μm to 1.00 μm.

SUMMARY OF THE INVENTION

As described in Yamagata factory report, “Commitment to manufacturing with high precision lens processing”, [online], CAPA camera net, [searched on Feb. 16, 2017], Internet <URL: http://capacamera.net/gmuseum/special/1301_2.html>, Dave Etchells, “The end of onion-ring bokeh? Panasonic beats the curse of aspheric lenses”, [online], May 2, 2014, IMAGING RESOURCE, [searched on Feb. 16, 2017], Internet <URL: http://www.imaging-resource.com/news/2014/05/02/the-end-of-onion-ring-bokeh-panasonic-beats-the-curse-of-aspheric-lenses>, and SEL2470GM Features, “A total of three aspheric lenses including the newly developed ultra-high aspheric XA (extreme aspherical) lenses are effectively arranged to realize sharp depiction from aperture opening”, [online], Sony Marketing Inc., [searched on Feb. 16, 2017], Internet <URL: http://www.sony.jp/ichigan/products/SEL2470GM/feature_1.html>, in a case of reducing the blurriness of the ring zone by smoothing the surface of the lens or the surface of the mold as much as possible, there is possibility of increasing the number of steps for processing a lens. Meanwhile, in the optical element for soft focus disclosed in each of JP1988-214715A (JP-563-214715A) and JP1989-147403A (JP-H01-147403A), the blurriness of the ring zone can be inconspicuous by roughening the optical surface to have an uneven shape of the same level as or more than an uneven shape of the optical surface which causes the blurriness of the ring zone. In this way, an effect of reducing the blurriness of the ring zone by roughening the optical surface can be obtained, but the purpose is to obtain a soft focus effect of reducing resolution of the entire image to be captured, and the application is limited to special imaging. Accordingly, effects of maintaining resolution of a screen with high definition and improving a blurred image that occurs before and behind a focal length cannot be obtained.

The present invention has been made in consideration of such circumstances, and an object thereof is to provide a lens, a zoom lens, and an imaging lens capable of eliminating blurriness of a ring zone without reducing resolution and increasing the number of steps for processing.

A lens according to an aspect of the present invention comprises random unevenness within an optical effective diameter of an optical surface, in which an arithmetic mean roughness within the optical effective diameter of the optical surface is 20 nm or more and 50 nm or less, and an average value of widths of protrusion portions of the unevenness on an average line of a roughness curve of the optical surface is 1/200 or more and 1/50 or less of the optical effective diameter of the optical surface.

A zoom lens according to another aspect of the present invention consists of, in order from an object side, a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming, a plurality of moving lens groups that move independently of each other during zooming, and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, in which the moving lens group includes at least one aspheric lens, and the aspheric lens is the above-described lens.

A zoom lens according to still another aspect of the present invention consists of, in order from an object side, a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming, a plurality of moving lens groups that move independently of each other during zooming, and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, in which one or both of the first stationary lens group and the second stationary lens group include at least one aspheric lens, and the aspheric lens is the above-described lens.

An imaging lens according to still another aspect of the present invention consists of, in order from an object side, a first lens group, a stop, and a second lens group having a positive refractive power, in which the first lens group is stationary with respect to an image plane during focus adjustment from an object at infinity to a close-range object, and the second lens group includes at least one aspheric lens, and the aspheric lens is the above-described lens.

According to the present invention, a lens, a zoom lens, and an imaging lens can be provided, which are capable of eliminating blurriness of a ring zone without reducing resolution and increasing the number of steps for processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an example of a lens for describing an embodiment of the present invention.

FIG. 2 is a schematic view of a roughness curve of an optical surface of the lens shown in FIG. 1.

FIG. 3 is a table showing shapes, blurred images, and visual sensory evaluation results of the blurred images of optical surfaces of lenses in Experiment Examples.

FIG. 4 is a table showing shapes, blurred images, and visual sensory evaluation results of the blurred images of optical surfaces of lenses in Experiment Examples.

FIG. 5 is a table showing shapes, blurred images, and visual sensory evaluation results of the blurred images of optical surfaces of lenses in Experiment Examples.

FIG. 6 is a table showing blurred images and visual sensory evaluation results of the blurred images of lenses in Experiment Examples.

FIG. 7 is a table showing shapes, visual sensory evaluation results of blurred images, and resolution evaluation results of optical surfaces of lenses in Experiment Examples.

FIG. 8 is a schematic view of a zoom lens comprising the lens of FIG. 1 in a state in which a focal length is at a wide angle end.

FIG. 9 is a schematic view of the zoom lens of FIG. 8 in a state in which the focal length is at an intermediate position between the wide angle end and a telephoto end.

FIG. 10 is a schematic view of the zoom lens of FIG. 8 in a state in which the focal length is at the telephoto end.

FIG. 11 is a schematic view of another zoom lens comprising the lens of FIG. 1 in a state in which a focal length is at a wide angle end.

FIG. 12 is a schematic view of the zoom lens of FIG. 11 in a state in which the focal length is at an intermediate position between the wide angle end and a telephoto end.

FIG. 13 is a schematic view of the zoom lens of FIG. 11 in a state in which the focal length is at the telephoto end.

FIG. 14 is a schematic view of still another zoom lens comprising the lens of FIG. 1 in a state in which a focal length is at a wide angle end.

FIG. 15 is a schematic view of the zoom lens of FIG. 14 in a state in which the focal length is at a telephoto end.

FIG. 16 is a schematic view of still another zoom lens comprising the lens of FIG. 1 in a state in which a focal length is at a wide angle end.

FIG. 17 is a schematic view of the zoom lens of FIG. 16 in a state in which the focal length is at a telephoto end.

FIG. 18 is a schematic view of an imaging lens comprising the lens of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows one example of a lens for describing an embodiment of the present invention, and FIG. 2 shows one example of a roughness curve of an optical surface of the lens of FIG. 1.

A lens 1 shown in FIGS. 1 and 2 is made of a resin material or a glass material. Examples of the resin material include cycloolefin polymers (COP), polymethyl methacrylate (PMMA), or the like. Examples of the glass material include quartz glass or the like.

The lens 1 has an optical surface 2. The optical surface 2 may be a convex curved surface, a concave curved surface, or a flat surface. The curved surface is not limited to a spherical surface, and may be an aspheric surface.

The lens 1 has random unevenness within the optical effective diameter D of the optical surface 2. Here, the optical effective diameter means the diameter of parallel rays that originates from an object point at infinity on the optical axis of the lens and passes through the lens. For example, the optical effective diameter can be set to be a value measured by a method based on a pinhole on a focal plane, which is defined in JIS B 7095. Moreover, random unevenness means that the unevenness arrangement has no regularity such as concentric or radial and the unevenness arrangement is irregular.

The arithmetic mean roughness Ra in the optical effective diameter D of the optical surface 2 which has random unevenness is set to be 20 nm or more and 50 nm or less. The arithmetic mean roughness Ra is determined by the method defined in JIS B 0601. That is, by measuring the cross-sectional curve of the optical surface 2 with a three-dimensional measurement machine (for example, UA3P manufactured by Panasonic Production Engineering Co., Ltd.), and applying a high pass filter (cutoff value λc) to the measured cross-sectional curve, a roughness curve in which the long wavelength component (undulating curve) is removed from the cross-sectional curve is obtained. The cutoff value λc is not particularly limited, but can be, for example, 8 mm at an effective diameter of 32 mm. Then, only the reference length L is extracted from the obtained roughness curve C1, and, as shown in the following expression, the absolute values of the deviation f(x) between the roughness curve C1 and the average line C2 (undulating curve representing the long wavelength component to be removed by the high pass filter) are summed up in the range of the extracted reference length L, and the value obtained by averaging the sums is taken as the arithmetic mean roughness Ra. The reference length L can be, for example, 8 mm.

Ra=1/L·∫|f(x)|dx

Furthermore, the average value of the widths W of the protrusion portions 3 of the unevenness on the average line C2 of the optical surface 2 is 1/200 or more and 1/50 or less of the optical effective diameter D of the optical surface 2. The protrusion portions 3 to provide the average value of the widths W are the protrusion portions 3 included in the reference length L extracted in a case of obtaining the arithmetic mean roughness Ra in the optical effective diameter D of the optical surface 2.

The unevenness of the optical surface 2 can be formed, for example, by etching the mold surface used for molding of the lens 1 to form unevenness, and transferring the unevenness of the mold surface to the lens material by molding. The unevenness of the optical surface 2 can also be formed by etching the optical surface 2.

With the lens 1 configured as described above, it is possible to reduce the blurriness of a ring zone appearing in a blurred image that occurs before and behind the focusing distance while maintaining the resolution of the screen with high definition. From the viewpoint of reducing the blurriness of the ring zone, it is preferable that the standard deviation of the widths W of the protrusion portion 3 is less than 1/125 of the optical effective diameter D of the optical surface 2. The protrusion portions 3 to provide the standard deviation of the widths W are the protrusion portions 3 included in the reference length L extracted in a case of obtaining the arithmetic mean roughness Ra in the optical effective diameter D of the optical surface 2. Furthermore, it is preferable that the arithmetic mean roughness Ra in the optical effective diameter D of the optical surface 2 is 20 nm or more and 30 nm or less, and the average value of the widths W of the protrusion portions 3 is 1/100 or more and 1/50 or less of optical effective diameter D of the optical surface 2.

The contrast of the ring zone that appears in the unevenness of the processing residual shape of the lens surface and the blurred image is theoretically considered in a document “Theory of bokeh image structure in camera lenses with an aspheric surface”, Optical Engineering, Vol. 53 (6), 2014. The document discloses that even the unevenness of the processing residual which does not affect the resolution of the lens has a great influence on the contrast of the ring zone of the blurred image. Yamagata factory report, “Commitment to manufacturing with high precision lens processing”, [online], CAPA camera net, [searched on Feb. 16, 2017], Internet <URL: http://capacamera.net/gmuseum/special/1301_2.html>, Dave Etchells, “The end of onion-ring bokeh? Panasonic beats the curse of aspheric lenses”, [online], May 2, 2014, IMAGING RESOURCE, [searched on Feb. 16, 2017], Internet <URL: http://www.imaging-resource.com/news/2014/05/02/the-end-of-onion-ring-bokeh-panasonic-beats-the-curse-of-aspheric-lenses>, and SEL2470GM Features “A total of three aspheric lenses including the newly developed ultra-high aspheric XA (extreme aspherical) lenses are effectively arranged to realize sharp depiction from aperture opening”, [online], Sony Marketing Inc., [searched on Feb. 16, 2017], Internet <URL: http://www.sony.jp/ichigan/products/SEL2470GM/feature_1.html> disclose that the contrast of the ring zone is reduced by suppressing the unevenness of the processing residual as much as possible. However, in the present invention, a method of reducing the contrast of the ring zone is implemented by providing the random unevenness that does not affect the resolution, even in a state where the processing residual is relatively large. Various studies have been conducted to examine the favorable condition. Specifically, in a case of giving an optional shape to the optical surface of the lens by applying the method described in the document “Theory of bokeh image structure in camera lenses with an aspheric surface”, Optical Engineering, Vol. 53 (6), 2014, a blurred image was generated by simulation, and the generated blurred image was visually sensory-evaluated. Hereinafter, an experiment example of the lens 1 will be described.

In the lens model used for simulation (hereinafter, simply referred to as a lens), the optical effective diameter D of the optical surface was set to be 58 mm, and a concentric protrusion shape having a height of 30 nm and a pitch of 2 mm was given to the optical surface in order to reproduce the optical surface on which blurriness of a ring zone occurs. This optical surface was subjected to random processing that gives random unevenness, and lenses were produced in which the arithmetic mean roughness Ra within the optical effective diameter of the optical surface, and the average value W_(AVG) and the standard deviation W_(SD) of the widths W of the protrusion portions were variously different. In the random processing, two parameters of the processing depth and the area ratio between a processed portion and an unprocessed portion (area of processed portion/area of unprocessed portion) were variously changed. In the simulation, in a state where the lens exit pupil position was 101 mm apart from the image focal plane to the object side, the exit pupil diameter was 53 mm, and the diameter of the ray incident on the lens was 58 mm, a blurred image was generated on the evaluation surface defocused by 11 mm from the image focal plane of the lens to the camera side.

In the visual sensory evaluation of the blurred image, based on the blurred image of the lens (processing depth=0, area ratio=0) of Experiment Example 1 in which the random processing was not performed, in a case where blurriness of a ring zone disappeared, the evaluation was regarded as “A”, in a case where the blurriness of the ring zone is locally remaining but the contrast of the blurriness of the ring zone is recognized to be reduced with respect to the reference blurred image, the evaluation was regarded as “B”, and in a case where the blurriness of the ring zone remains as a whole and the contrast of the blurriness of the ring zone is not recognized to be reduced with respect to the reference blurred image, the evaluation was regarded as “C”.

FIGS. 3 to 6 show shapes of the optical surfaces of the lenses of the experiment examples, blurred images generated by simulation, and the results of visual sensory evaluation of the blurred images.

In the lenses of Experiment Examples 1 to 4, the arithmetic mean roughness Ra in the optical effective diameter was less than 20 nm, the visual sensory evaluation results thereof were all “C”, and regardless of how the ratio (W_(AVG)/D) of the average value W_(AVG) of the widths W of the protrusion portions with respect to the optical effective diameter D was set, the blurriness of the ring zone remained. In addition, in the lenses of Experiment Examples 20 and 21, the arithmetic mean roughness Ra exceeded 50 nm, the visual sensory evaluation results thereof were all “A”, and regardless of the W_(AVG)/D, the blurriness of the ring zone disappeared. On the other hand, in the lenses of Experiment Examples 5 to 19, the arithmetic mean roughness Ra was 20 nm or more and 50 nm or less, and in these cases, the reduction effect of the blurriness of the ring zone was changed in accordance with the W_(AVG)/D. For example, the visual sensory evaluation results of the lenses of Experiment Examples 9, 14, and 19 having the W_(AVG)/D of 1/500 were “C”, and the visual sensory evaluation results of the lenses of Experiment Examples 5, 10, and 15 having the W_(AVG)/D of 1/20 were also “C”. On the other hand, the visual sensory evaluation results of Experiment Examples 6 to 8, 11 to 13, and 16 to 18 having the W_(AVG)/D of 1/200 or more and 1/50 or less were “A” or “B”. From the above, it can be understood that, in a case where the arithmetic mean roughness Ra is 20 nm or more and 50 nm or less, by setting the W_(AVG)/D to 1/200 or more and 1/50 or less, the blurriness of the ring zone can be eliminated or reduced, and it is preferable that the W_(AVG)/D is 1/100 or more and 1/50 or less. Further, in the lenses of Experiment Examples 23 to 25, the ratio (W_(SD)/D) of the standard deviation W_(SD) of the widths W of the protrusion portions to the optical effective diameter D was made to be different by setting the arithmetic mean roughness Ra to 20 nm or more and 50 nm or less. As the W_(SD)/D increases, the W_(AVG)/D increases, and thus in the lens of Experiment Example 25 in which the W_(SD)/D is 1/125, the W_(AVG)/D exceeded 1/50. Therefore, it is preferable that the W_(SD)/D is 0 or more and less than 1/125.

Next, in a single-focus lens unit with a focal length of 100 mm and a T value of 2.0 (composition of 11 lenses), a lens (in which the outer diameter is 60.5 mm, the curvature radius of the surface on the object side is 148.68 mm, and the surface on the image side is flat) which is disposed closest to the image side was replaced with an aspheric lens on which the above-mentioned random processing was performed, or an aspheric lens on which the above-mentioned random processing was not performed, and visual sensory evaluation and resolution evaluation of a blurred image were performed. For visual sensory evaluation of the blurred image, a point light source was placed at a distance of 3 m from the object side of the lens, the focus of the lens was adjusted to infinity to image the point light source, and the captured blurred image was visually sensory-evaluated. In visual sensory evaluation of the captured blurred image, the evaluation standards of “A” evaluation, “B” evaluation, and “C” evaluation were the same as the evaluation standard of visual sensory evaluation of the blurred image in the simulation described above. In addition, resolution evaluation was performed using a modulation transfer function (MTF) measurement machine (manufactured by FK Optical Co., Ltd.: matrix MTF measurement device), and an MTF value measured at a spatial frequency of 40 lp/mm at the central angle of view of the lens unit was regarded as an evaluation value of the resolution. Then, based on the MTF value of the aspheric lens that was not subjected to random processing, in a case where the resolution deterioration rate is 0% or more and less than 3%, the evaluation was regarded as “A”, in a case where the resolution deterioration rate is 3% or more and less than 6%, the evaluation was regarded as “B”, and in a case where the resolution deterioration rate was 6% or more, the evaluation was regarded as “C”.

FIG. 7 shows the shapes of the optical surfaces of the lenses of the experiment examples, and the results of visual sensory evaluation and resolution evaluation of the captured blurred images.

The resolution evaluation of the lens of Experiment Example 29 in which the arithmetic mean roughness Ra was 100 nm was “C” evaluation. As described above, in a case where the arithmetic mean roughness Ra exceeds 50 nm, the blurriness of the ring zone disappeared regardless of the ratio (W_(AVG)/D) of the average value W_(AVG) of the widths W of the protrusion portions to the optical effective diameter D, but resolution also deteriorated. On the other hand, the resolution evaluation of the lens of Experiment Example 28 in which the arithmetic mean roughness Ra was 50 nm was “B” evaluation, and the resolution evaluation of the lens of Experiment Example 27 in which the arithmetic mean roughness Ra was 20 nm to 30 nm was “A” evaluation. The visual sensory evaluations of the lenses of Experiment Examples 27 and 28 were all “A” evaluation. From the above, it can be found that, by setting the arithmetic mean roughness Ra to 20 nm or more and 50 nm or less, reduction of the blurriness of the ring zone and maintenance of screen resolution can be both achieved. Preferably the arithmetic mean roughness Ra is 20 nm or more and 30 nm or less.

Next, a zoom lens and an imaging lens comprising the lens 1 shown in FIGS. 1 and 2 will be described.

FIGS. 8 to 10 show an example of the zoom lens comprising the lens 1.

FIG. 8 shows a state in which a focal length is at a wide angle end, FIG. 9 shows a state in which the focal length is at an intermediate position between the wide angle end and a telephoto end, and FIG. 10 shows a state in which the focal length is at the telephoto end. In FIGS. 8 to 10, it should be noted that the left side is the object side and the right side is the image plane side, and the illustrated aperture stop St does not necessarily represent the size or the shape thereof, and just indicates a position of the aperture stop on the optical axis Z. Further, in the light path diagram of FIG. 8, the movement locus of each lens group during zooming, the on-axis rays wa and the ray wb of the maximum angle of view are shown together.

The zoom lens 10 shown in FIGS. 8 to 10 is substantially composed of, in order from the object side, a first lens group G1 that remains stationary during zooming and has a positive refractive power, a plurality of moving lens groups that move independently of each other by changing distances between groups adjacent to each other in a direction of an optical axis during zooming, and a final lens group that has a positive refractive power, is disposed closest to the image side, and remains stationary during zooming. In the examples shown in FIGS. 8 to 10, the zoom lens 10 is composed of the first lens group G1 that has a positive refractive power and remains stationary during zooming, second to fourth lens groups G2 to G4 (moving lens groups) that move independently of each other by changing distances between groups adjacent to each other in a direction of an optical axis during zooming, and a fifth lens group G5 (final lens group) that has a positive refractive power, is disposed closest to the image side, and remains stationary during zooming. The first lens group G1 is composed of ten lenses L1 a to L1 j, the second lens group G2 is composed of one lens L2 a, the third lens group G3 is composed of five lenses L3 a to L3 e, the fourth lens group G4 is composed of two lenses L4 a and L4 b, and the fifth lens group G5 is composed of 12 lenses L5 a to L51.

In a case of applying the zoom lens 10 to an imaging apparatus, it is preferable to dispose a cover glass, a prism, and various filters such as an infrared cut filter and a low pass filter between the optical system and the image plane Sim according to the configuration of the camera on which the lens is mounted. Therefore, FIGS. 8 to 10 show an example in which parallel flat plate-like optical members PP1 and PP2 assumed as the above members are disposed between the lens system and the image plane Sim.

As described above, by setting the first lens group G1 closest to the object side to have a positive refractive power, it is possible to shorten the total length of the lens system, and thus it is advantageous in reducing the size. In addition, by setting the first lens group G1 closest to the image side to have a positive refractive power, it is possible to suppress an increase in incident angle of the principal ray of the off-axis rays incident onto the image plane Sim, which makes it possible to suppress shading. Furthermore, since the lens group closest to the object side and the lens group closest to the image side remain stationary during zooming and the total length of the lens system does not change, it is possible to obtain the zoom lens having a small change in the center of gravity during zooming and good operability.

The plurality of moving lens groups are composed of, in order from the object side, a lens group having a positive refractive power, a lens group having a negative refractive power, and a lens group having a negative refractive power. In general, the moving amount of the moving lens group having a negative refractive power can be smaller in a case where the number of the moving lens groups is two than in a case where the number is one. Therefore, the above-mentioned composition can result in reduction in the total length of the lens system. Since the image height can be lowered by including the moving lens group having a positive refractive power, the effective diameter of the first lens group G1 on the telephoto side can be suppressed. From the above, the size and weight of the whole zoom lens can be reduced.

The first lens group G1 has at least two negative lenses, and the negative lens closest to the object side has a meniscus shape convex toward the object side, and the first n lens, which is at least one negative lens of the second and subsequent negative lenses, is composed to satisfy following Conditional Expressions (1) and (2). In FIGS. 8 to 10, the lens L1 c corresponds to the first n lens.

As described above, by arranging at least two negative lenses in the first lens group G1, it is possible to obtain a negative refractive power necessary for achieving the wide angle. The negative lens of the first lens group G1, which is closest to the object side, has a meniscus shape convex toward the object side, which makes it possible to suppress the occurrence of astigmatism and distortion. Further, the arrangement of the first n lens satisfying the following Conditional Expressions (1) and (2) in the first lens group G1 makes it possible to make good correction of chromatic aberration of the first lens group G1, and in particular, to make good correction of lateral chromatic aberration on the wide angle side and make correction of longitudinal chromatic aberration on the telephoto side.

By satisfying Conditional Expression (1), lateral chromatic aberration on the wide angle side and longitudinal chromatic aberration on the telephoto side during focusing can be favorably corrected. Further, by satisfying Conditional Expression (2) together with Conditional Expression (1), the secondary spectrum can be favorably corrected.

62<νdn . . .   (1)

0.64<θgFn+0.001625×νdn<0.7 . . .   (2)

-   -   here,     -   νdn: Abbe number of the first n lens at a d line     -   θgFn: Partial dispersion ratio of the first n lens

Next, numerical examples of the zoom lens 10 will be described. Table 1 shows basic lens data of the zoom lens 10, Table 2 shows data on specification, Table 3 shows data on changing surface distance, and Table 4 shows data on aspheric surface coefficients.

In the lens data of Table 1, the column of the surface number shows surface numbers that increase sequentially toward the image plane side, with the surface of an element closest to the object side being regarded as the first surface. The column of the curvature radius shows curvature radii of the respective surfaces. The column of the surface distance shows surface distances on the optical axis Z between the respective surfaces and the next surfaces. The column of nd shows the refractive indexes of respective optical elements at a d line (a wavelength of 587.6 nm), the column of νd shows Abbe numbers of respective optical elements at the d line (a wavelength of 587.6 nm), and the column of θgF shows the partial dispersion ratios of respective optical elements.

The partial dispersion ratio θgF is expressed by the following expression.

θgF=(Ng−NF)/(NF−NC)

-   -   here,     -   Ng: refractive index at a g line     -   NF: refractive index at an F line     -   NC: refractive index at a C line

Here, reference signs of curvature radii are set to be positive in a case where the surface shapes are convex toward the object side, and reference signs of curvature radii are set to be negative in a case where of the surface shapes are convex toward the image plane side. The basic lens data includes an aperture stop St and optical members PP1 and PP2. In the column of a surface number of a surface corresponding to the stop St, the surface number and a term of (stop) are noted. Further, in the lens data of Table 1, DD [surface number] is described in the place of the surface distance in which the distance changes during zooming. The numerical values corresponding to DD [surface number] are shown in Table 3.

Values of a zoom magnification, a focal length f′, an F value FNo., a total angle of view 2ω are shown in data on the specification in Table 2.

In the lens data of Table 1, the reference sign * is attached to surface numbers of aspheric surfaces, and numerical values of the paraxial curvature radii are shown as the curvature radius of the aspheric surface. The data on the aspheric surface coefficients in Table 4 show surface numbers for the aspheric surfaces and the aspheric surface coefficients for the aspheric surfaces. The aspheric surface coefficients are values of the coefficients KA and Am (m=3 . . . 20) in aspheric surface expression represented as the following expression.

Zd=C·h ²/{1+(1−KA·C ² ·h ²)^(1/2) }+ΣAm·h ^(m)

-   -   here,     -   Zd: aspheric surface depth (a length of a perpendicular drawn         from a point on an aspheric surface at height h to a plane that         is perpendicular to the optical axis that contacts the vertex of         the aspheric surface)     -   h: height (a distance from the optical axis)     -   C: reciprocal of paraxial curvature radius     -   KA, Am: aspheric surface coefficient (m=3 . . . 20)

In the basic lens data, the data on specification, and the data on changing surface distance, a degree is used as a unit of an angle, and mm is used as a unit of a length, but since the optical system can be used with magnification and reduction in proportion, appropriate different units may be used.

TABLE 1 Surface Curvature Surface Number Radius Distance nd vd θgF 1 214.0485 3.6001 1.88300 40.76 0.56679 2 75.1630 22.9827 3 −597.4831 3.3000 1.73400 51.47 0.54874 4 443.5473 12.9081 5 −187.4186 5.8583 1.53775 74.70 0.53936 6 122.1466 14.7216 1.91650 31.60 0.59117 7 −1192.6629 2.6958 *8 337.3004 13.7943 1.43875 94.94 0.53433 9 −172.5134 13.4076 10 192.0693 17.0129 1.49700 81.54 0.53748 11 −139.9406 0.6538 12 −133.1303 3.3500 1.85150 40.78 0.56958 13 115.2733 15.2541 1.49700 81.54 0.53748 14 −398.0807 6.0395 15 459.0857 12.9020 1.53775 74.70 0.53936 16 −156.6756 0.2000 17 137.1994 15.6658 1.49700 81.54 0.53748 18 −276.3776 DD [18] 19 362.4361 2.9957 1.49700 81.54 0.53748 20 −555.5230 DD [20] *21 212.6957 2.4011 1.53775 74.70 0.53936 22 27.2627 10.4426 23 −42.9639 1.2004 2.00100 29.13 0.59952 24 191.3068 2.4309 25 −105.3359 6.7325 1.69895 30.13 0.60298 26 −28.8119 2.4783 1.69560 59.05 0.54348 27 −82.6623 0.3007 28 161.3383 5.2491 1.83481 42.72 0.56486 29 −80.5118 DD [29] 30 −52.0619 1.3100 1.49700 81.54 0.53748 31 1116.7924 1.9941 1.84666 23.83 0.61603 32 −307.6714 DD [32] 33 (stop) ∞ 1.8275 34 118.3571 3.8140 1.91082 35.25 0.58224 35 −350.3523 2.5727 36 −105.5123 3.0000 1.76182 26.52 0.61361 37 −208.3315 11.3437 38 59.9113 5.2848 1.65844 50.88 0.55612 39 ∞ 0.3009 40 42.0799 10.3271 1.43875 94.94 0.53433 41 −78.3277 1.5500 1.95375 32.32 0.59015 42 56.6019 4.9263 43 −226.8790 6.1786 1.80518 25.43 0.61027 44 −36.3203 1.4100 1.80400 46.58 0.55730 45 −106.9554 0.4084 46 64.4975 7.8638 1.48749 70.24 0.53007 47 −64.4975 0.2001 48 54.5207 2.0998 1.91082 35.25 0.58224 49 20.5114 13.6195 1.49700 81.54 0.53748 50 −42.0493 1.6000 1.90043 37.37 0.57720 51 57.4339 0.6085 52 48.2644 3.3704 1.84666 23.83 0.61603 53 240.7851 3.0000 54 ∞ 1.4000 1.51633 64.14 0.53531 55 ∞ 1.0000 56 ∞ 3.6900 1.51633 64.14 0.53531 57 ∞ 54.0311

TABLE 2 Wide Telephoto Angle End Intermediate End Zoom 1.0 2.4 7.4 Magnification F′ 19.91 46.80 146.33 FNo. 2.86 2.86 2.86 2ω [°] 73.6 33.2 11.0

TABLE 3 Wide Telephoto Angle End Intermediate End DD [18] 1.4993 49.5135 85.3829 DD [20] 1.4865 6.8361 8.7457 DD [29] 62.9756 9.2695 21.2659 DD [32] 52.4033 52.7456 2.9702

TABLE 4 Surface Number 8 KA   1.0000000E+00 A3   1.5064530E−07 A4 −1.5641141E−07 A5   1.6501598E−09 A6 −3.9701428E−11 A7   6.9263338E−13 A8   1.0556630E−17 A9 −7.0509369E−17 A10   5.3287613E−19 Surface Number 21 KA   1.0000000E+00 A4   1.5045420E−06 A6 −4.1679388E−10 A8 −8.9800509E−12 A10   7.0993908E−14 A12 −3.2299521E−16 A14   8.7823289E−19 A16 −1.4036759E−21 A18   1.2097861E−24 A20 −4.3023907E−28

Here, it is preferable that the first lens group G1 and the fifth lens group G5, which are stationary lens groups, includes at least one aspheric lens, and the aspheric lens is the lens 1 shown in FIGS. 1 and 2. At the telephoto end, the on-axis rays wa is relatively thick in the first lens group G1 and the fifth lens group G5 and the aspheric lens composed of the lens 1 is included in the first lens group G1 and/or the fifth lens group G5, which makes it possible to effectively reduce the blurriness of the ring zone at telephoto end. In the lens data of Table 1, the lens L1 e of the first lens group G1 having an aspheric optical surface indicated by surface number 8 and the lens L3 a of the third lens group G3 having an aspheric optical surface indicated by surface number 21 are composed of the lens 1.

FIGS. 11 to 13 show another example of the zoom lens comprising the lens 1.

FIG. 11 shows a state in which a focal length is at a wide angle end, FIG. 12 shows a state in which the focal length is at an intermediate position between the wide angle end and a telephoto end, and FIG. 13 shows a state in which the focal length is at the telephoto end. In FIGS. 11 to 13, it should be noted that the left side is the object side and the right side is the image plane side, and the illustrated aperture stop St does not necessarily represent the size or the shape thereof, and just indicates a position of the aperture stop on the optical axis Z. Further, in the light path diagram of FIG. 11, the on-axis rays wa and the rays wb at the maximum angle of view, the movement locus of each lens group during zooming (arrows in the figure), and the point at which the imaging magnification is −1 (a horizontal dotted line in the figure) are shown together.

As shown in FIGS. 11 to 13, the zoom lens 20 consists of, in order from the object side along the optical axis Z, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, a third lens group G3 having a positive refractive power, a fourth lens group G4 having a positive refractive power, an aperture stop St, and a fifth lens group G5 having a positive refractive power.

In a case of applying the zoom lens 20 to an imaging apparatus, it is preferable to dispose a cover glass, a prism, and various filters such as an infrared cut filter and a low pass filter, between the optical system and the image plane Sim according to the configuration of the camera on which the lens is mounted. Therefore, FIGS. 11 to 13 show an example in which parallel flat plate-like optical members PP1 to PP3 assumed as the above members are disposed between the lens system and the image plane Sim.

Further, during zooming, the first lens group G1 and the fifth lens group G5 are configured to remain stationary with respect to the image plane Sim, and the second lens group G2, the third lens group G3, and the fourth lens group G4 are configured to move independently of each other so as to change the distance therebetween, and during zooming from the wide angle end to the telephoto end, the second lens group G2 is configured to move from the object side to the image plane side.

The second lens group G2 is configured to comprise at least four negative lenses including three negative lenses arranged successively from the object side and at least one positive lens. As described above, by assigning the negative refractive power of the second lens group G2 to four or more negative lenses, it is possible to suppress fluctuations in spherical aberration and distortion during zooming, which is advantageous for increasing the magnification. In addition, since the refractive powers of the negative lens and the positive lens can be increased while maintaining the refractive power of the second lens group G2, even in a case where the Abbe number difference between the positive lens and the negative lens is not set to be large in consideration of 2nd chromatic aberration correction, fluctuations of longitudinal chromatic aberration and lateral chromatic aberration during zooming can be suppressed. Furthermore, by making three negative lenses be arranged successively in order from the object side of the second lens group G2 and concentrating the negative refractive power on the object side of the second lens group G2, the angle formed by the principal ray of the periphery angle of view, which is incident on subsequent lenses, and the optical axis at the wide angle end can be reduced, which is advantageous for achieving the wide angle. Also, deteriorations of distortion and astigmatism at the time of increasing magnification can be prevented, and astigmatism likely to be generated by the first lens group G1 can be corrected at the wide angle end.

Assuming that the lens closest to the object side among these negative lenses is the L21 negative lens, a configuration for satisfying following Conditional Expressions (3) and (4) is established. By not allowing the value of Conditional Expression (3) to be equal to or less than the lower limit, it is possible to suppress fluctuations in 1st-order lateral chromatic aberration and 1st-order longitudinal chromatic aberration during zooming. By not allowing the value of Conditional Expression (3) to be equal or larger than the upper limit, it is possible to correct 2nd lateral chromatic aberration at the wide angle end which occurs in the first lens group G1 at the time of correcting 2nd longitudinal chromatic aberration at the telephoto end, and it is possible to well-balancedly correct 2nd longitudinal chromatic aberration at the telephoto end, lateral chromatic aberration at the telephoto end, and 2nd lateral chromatic aberration at the wide angle end.

The effect of the lower limit of Conditional Expression (3) can be made more remarkable by not allowing the value of Conditional Expression (3) to be equal to or less than the lower limit and not allowing the value of Conditional Expression (4) to be equal to or less than the lower limit. By not allowing the value of Conditional Expression (4) to be equal to or greater than the upper limit, it is possible to prevent distortion at the wide angle end from deteriorating.

25<νd21<45 . . .   (3)

0.31<f2/f21<0.7 . . .   (4)

-   -   here,     -   νd21: Abbe number of the L21 negative lens at the d line     -   f2: focal length of the second lens group at the d line     -   f21: focal length of the L21 negative lens at the d line

Next, numerical examples of the zoom lens 20 will be described. Table 5 shows basic lens data of the zoom lens 20, Table 6 shows data on specification, Table 7 shows data on changing surface distance, and Table 8 shows data on aspheric surface coefficients.

In the lens data of Table 6, the column of the surface number shows surface numbers that increase sequentially toward the image plane side, with the surface of an element closest to the object side being regarded as the first surface. The column of the curvature radius shows curvature radii of the respective surfaces. The column of the surface distance shows surface distances on the optical axis Z between the respective surfaces and the next surfaces. The column of nd shows the refractive indexes of respective optical elements at a d line (a wavelength of 587.6 nm), and the column of νd shows Abbe numbers of respective optical elements at the d line (a wavelength of 587.6 nm), and the column of θg,f shows the partial dispersion ratios of respective optical elements.

The partial dispersion ratio θg,f is expressed by the following expression.

θg,f=(Ng−NF)/(NF−NC)

-   -   here,     -   Ng: refractive index at the g line     -   NF: refractive index at the F line     -   NC: refractive index at the C line

Here, reference signs of curvature radii are set to be positive in a case where the surface shapes are convex toward the object side, and reference signs of curvature radii are set to be negative in a case where of the surface shapes are convex toward the image plane side. The basic lens data includes an aperture stop St and optical members PP1 to PP3. In the column of a surface number of a surface corresponding to the stop St, the surface number and a term of (stop) are noted. Further, in the lens data of Table 6, DD [surface number] is described in the place of the surface distance in which the distance changes during zooming. The numerical values corresponding to DD [surface number] are shown in Table 8.

Values of a zoom magnification, a focal length f′, a back focus Bf′, an F value FNo., and a total angle of view 2ω are shown in data on the specification in Table 7.

In the lens data of Table 6, the reference sign * is attached to surface numbers of aspheric surfaces, and numerical values of the paraxial curvature radii are shown as the curvature radius of the aspheric surface. The data on the aspheric surface coefficients in Table 8 show surface numbers for the aspheric surfaces and the aspheric surface coefficients for the aspheric surfaces. The aspheric surface coefficients are values of the coefficients KA and Am (m=3 . . . 20) in aspheric surface expression represented as the following expression.

Zd=C·h ²/{1+(1−KA·C ² ·h ²)^(1/2) }+ΣAm·h ^(m)

-   -   here,     -   Zd: aspheric surface depth (a length of a perpendicular drawn         from a point on an aspheric surface at height h to a plane that         is perpendicular to the optical axis that contacts the vertex of         the aspheric surface)     -   h: height (a distance from the optical axis)     -   C: reciprocal of paraxial curvature radius     -   KA, Am: aspheric surface coefficient (m=3 . . . 20)

In the basic lens data, the data on specification, and the data on changing surface distance, a degree is used as a unit of an angle, and mm is used as a unit of a length, but since the optical system can be used with magnification and reduction in proportion, appropriate different units may be used.

TABLE 5 Surface Curvature Surface Number Radius Distance nd νd θg,f  1 2149.2163 4.4000 1.83400 37.16 0.57759  2 364.4008 1.8100  3 357.1559 24.5800 1.43387 95.18 0.53733  4 −629.0299 32.8500  5 363.8700 15.6200 1.43387 95.18 0.53733  6 ∞ 0.1200  7 310.1672 17.8400 1.43387 95.18 0.53733  8 ∞ 2.9000  9 173.0993 14.6700 1.43875 94.94 0.53433  10 310.0848 DD[10] *11 109963.7968 2.8000 1.90366 31.31 0.59481  12 56.5266 8.6300  13 −84.6070 1.6000 2.00100 29.13 0.59952  14 321.4052 6.6700  15 −62.2824 1.6000 1.95375 32.32 0.59015  16 115.4560 6.9400 1.89286 20.36 0.83944  17 −73.9497 0.1200  18 962.3821 7.7100 1.80518 25.43 0.61027  19 −51.3780 1.6200 1.80400 46.58 0.55730  20 2303.8825 DD[20]  21 170.3657 9.7800 1.49700 81.54 0.53748 *22 −209.1383 DD [22]  23 137.4359 11.9100 1.43700 95.10 0.53364  24 −175.8090 2.0000 1.59270 35.31 0.59336  25 −597.2019 0.2500 *26 188.3526 9.3100 1.43700 95.10 0.53364  27 −195.4929 0.1200  28 247.3158 2.0000 1.80000 29.84 0.60178  29 94.0850 12.0500 1.43700 95.10 0.53364  30 −217.6314 DD [30]  31(stop) ∞ 5.0700  32 −188.3440 1.4000 1.77250 49.60 0.55212  33 62.0923 0.1200  34 43.4903 4.5500 1.80518 25.42 0.61616  35 151.4362 2.0300  36 −188.3403 1.4000 1.48749 70.24 0.53007  37 72.1812 9.2600  38 −50.3918 3.2500 1.80440 39.59 0.57297  39 63.9801 8.1300 1.80518 25.43 0.61027  40 −46.8126 0.3400  41 −50.8827 1.6600 1.95375 32.32 0.59015  42 56.9580 7.3800 1.72916 54.68 0.54451  43 −73.6910 0.1200  44 215.7126 10.9800 1.73800 32.26 0.58995  45 −215.7126 8.8100  46 182.7540 17.0600 1.67003 47.23 0.56276  47 −103.9363 0.1200  48 148.7010 2.9000 1.95375 32.32 0.59015  49 44.8210 0.8500  50 44.9406 10.1300 1.51633 64.14 0.53531  51 −64.7286 0.1200  52 65.6410 5.1900 1.48749 70.24 0.53007  53 −65.6410 1.8500 1.95375 32.32 0.59015  54 ∞ 0.2500  55 ∞ 1.0000 1.51633 64.14 0.53531  56 ∞ 0.0000  57 ∞ 33.0000 1.60863 46.60 0.56787  58 ∞ 13.2000 1.51633 64.14 0.53531  59 ∞ 17.3299

TABLE 6 Wide Angle Telephoto End Intermediate End Zoom 1.0 48.0 77.0 Magnification f′ 9.30 446.26 715.88 Bf′ 47.46 47.46 47.46 FNo. 1.76 2.27 3.64 2ω[°] 65.0 1.4 0.8

TABLE 7 Wide Angle Telephoto End Intermediate End DD[10] 2.8554 186.6407 191.1526 DD[20] 291.2076 26.4986 3.9764 DD[22] 1.4039 6.7033 1.9940 DD[30] 3.1233 78.7475 101.4671

TABLE 8 Surface Number 11 22 26 KA   1.0000000E+00   1.0000000E+00   1.0000000E+00 A3 −1.8505954E−21 −7.1721817E−22   6.6507804E−22 A4   4.0660287E−07   1.6421968E−07 −2.8081272E−07 A5 −6.4796240E−09 −5.6511999E−09 −8.0962001E−09 A6   8.4021729E−10   1.7414539E−10   2.8172499E−10 A7 −4.5016908E−11   7.4176985E−13 −1.6052722E−12 A8   4.3463314E−13 −9.7299399E−14 −1.0541094E−13 A9   3.5919548E−14   1.1281878E−15   2.1399424E−15 A10 −8.9257498E−16 −4.4848875E−19 −1.0917621E−17

Here, it is preferable that the third lens group G3 and the fourth lens group G4, which are moving lens groups, include at least one aspheric lens, and the aspheric lens is the lens 1 shown in FIGS. 1 and 2. The on-axis rays wa is relatively thick in the third lens group G3 and the fourth lens group G4 and the aspheric lens composed of the lens 1 is included in the third lens group G3 and/or the fourth lens group G4, which makes it possible to effectively reduce the blurriness of the ring zone in any zoom range from the wide angle end to the telephoto end. In the lens data of Table 5, the lens L21 of the second lens group G2 having an aspheric optical surface indicated by surface number 11, the lens L31 of the third lens group G3 having an aspheric optical surface indicated by surface number 22, and the lens L43 of the fourth lens group G4 having an aspheric optical surface indicated by surface number 26 are composed of the lens 1.

FIGS. 14 and 15 show another example of the zoom lens comprising the lens 1.

FIG. 14 shows the state in which the focal length is at the wide angle end, and FIG. 15 shows the state in which the focal length is at the telephoto end. In FIGS. 14 and 15, an object at infinity is in focus, the left side is an object side, and the right side is an image side. In FIG. 14, the on-axis rays B0 w and the off-axis rays B1 w with the maximum angle of view at the wide angle end state are shown as the light paths, and in FIG. 15, the on-axis rays B0 t and the off-axis rays B1 t with the maximum angle of view at the telephoto end state are shown as the light paths.

The zoom lens 30 substantially consists of, in order from the object side to the image side along the optical axis Z, a first lens group G1 that has a positive refractive power and remains stationary with respect to an image plane Sim during zooming, a second lens group G2 that has a negative refractive power and moves in a direction of an optical axis during zooming, a third lens group G3 that has a negative refractive power and moves in the direction of the optical axis during zooming, an aperture stop St, and a fourth lens group G4 that has a positive refractive power and remains stationary with respect to the image plane Sim during zooming. It should be noted that the aperture stop St shown in FIGS. 14 and 15 does not necessarily represent the size or the shape thereof, and indicates a position of the stop on the optical axis Z.

In a case of applying the zoom lens 30 to an imaging apparatus, it is preferable to provide various filters, prisms, and/or a protective cover glass based on specification of the imaging apparatus. Therefore, FIGS. 14 and 15 show an example in which parallel flat plate-like optical members P1 to P3 assumed as the above members are disposed between the lens system and the image plane Sim. However, positions of the optical members P1 to P3 are not limited to those shown in FIGS. 14 and 15, and it is also possible to adopt a configuration in which at least one of the optical members P1 to P3 is omitted.

In the zoom lens 30, the second lens group G2 has a main zooming function, and the third lens group G3 performs correction of focal shift caused by zooming. During zooming from the wide angle end to the telephoto end, the second lens group G2 moves to the image side, the third lens group G3 moves to the object side, and then moves to the image side. The arrows below the second lens group G2 and the third lens group G3 in the upper part of FIG. 14 indicate the schematic movement loci of these lens groups during zooming from the wide angle end to the telephoto end.

The first lens group G1 substantially consists of, in order from the object side, a front group of the first lens group G1A that has a negative refractive power and remains stationary with respect to the image plane Sim during focusing, an intermediate group of the first lens group G1B that has a positive refractive power and moves to the image side during focusing from a distant object to a close-range object, and a rear group of the first lens group G1C that has a positive refractive power and remains stationary with respect to the image plane Sim during focusing. With such a configuration, it is possible to achieve the wide angle while favorably suppressing change (bleeding) in angle of view during focusing. The arrow below the intermediate group of the first lens group G1B in the upper part of FIG. 14 indicates the moving direction of the lens group during focusing from a distant object to a close-range object.

In the example shown in FIGS. 14 and 15, the front group of the first lens group G1A consists of four lenses LA1 to LA4 in order from the object side, the intermediate group of the first lens group G1B consists of only one lens LB1, and the rear group of the first lens group G1C consists of six lenses LC1 to LC6 in order from the object side.

The front group of the first lens group G1A is composed to include a plurality of negative lenses that are arranged successively from a position closest to the object side and a positive lens that is disposed to be closest to the image side. To provide a negative refractive power to a position closest to the object side is an advantageous in achieving the wide angle. To assign the negative refractive power on the object side to the plurality of negative lenses is advantageous in favorably correcting spherical aberration and off-axis aberrations caused by achieving the wide angle. In addition, since the front group of the first lens group G1A includes not only a negative lens but also a positive lens, chromatic aberration is easily balanced.

The front group of the first lens group G1A may be composed to substantially consist of, in order from the object side, two negative meniscus lenses convex toward the object side, a negative lens, and a positive lens. In such a case, it is possible to correct the spherical aberration on the telephoto side while suppressing fluctuation in off-axis aberrations caused by zooming and particularly suppressing fluctuation in distortion and/or suppressing fluctuation in field curvature.

The intermediate group of the first lens group G1B may be composed to substantially consist of only one positive lens. In such a case, since it is possible to ensure the amount of movement of the lens which moves during focusing, it becomes easy to suppress fluctuation in spherical aberration caused by focusing. In addition, it is possible to reduce the weight of the lens group that moves during focusing.

The rear group of the first lens group G1C is composed to include one or more negative lenses having concave surface facing toward the object side. With this configuration, it is possible to effectively correct spherical aberration occurring on the telephoto side.

It is preferable that the rear group of the first lens group G1C has, successively in order from the position closest to the object side, a biconvex lens, and a negative meniscus lens having concave surface facing toward the object side. In such a case, it is possible to effectively correct field curvature on the wide angle side while correcting spherical aberration on the telephoto side.

The rear group of the first lens group G1C may be composed to substantially consist of, in order from the object side, a biconvex lens, a negative meniscus lens having concave surface facing toward the object side, a cemented lens in which a negative lens and a positive lens are cemented in order from the object side, and one or more positive lenses. In such a case, the positive spherical aberration generated by the negative refractive power of the front group of the first lens group G1A can be corrected by the positive lens in the rear group of the first lens group G1C, and the negative spherical aberration that is overcorrected can be corrected by the cemented surface of the cemented lens in the rear group of the first lens group G1C. The rear group of the first lens group G1C has, in order from the object side, a biconvex lens and a negative meniscus lens having concave surface facing toward the object side, which makes it possible to effectively correct field curvature on the wide angle side while correcting spherical aberration.

In a case where the rear group of the first lens group G1C substantially consist of, in order from the object side, a biconvex lens, a negative meniscus lens having concave surface facing toward the object side, a cemented lens in which a negative lens and a positive lens are cemented in order from the object side, and one or more positive lenses, the rear group of the first lens group G1C may be composed to substantially consist of six lenses. That is, the rear group of the first lens group G1C may be composed to substantially consist of, in order from the object side, a biconvex lens, a negative meniscus lens having concave surface facing toward the object side, a cemented lens in which a negative lens and a positive lens are cemented in order from the object side, and two positive lenses. In such a case, it is advantageous in correcting spherical aberration more favorably than the case where the rear group of the first lens group G1C has only one positive lens closer to the image side than the cemented lens, and for reduction in size and cost of the lens system as compared with the case where the rear group of the first lens group G1C has three or more positive lenses closer to the image side than the cemented lens.

Then, the zoom lens is composed to satisfy Conditional Expression (5).

65<νn1A2<110  (5)

-   -   here,     -   νn1A2: an Abbe number of a second negative lens from the object         side in the front group of the first lens group at the d line

By satisfying Conditional Expression (5), it is possible to suppress lateral chromatic aberration occurring in the entire zoom range, particularly in the peripheral portion of the imaging region. By not allowing the value of Conditional Expression (5) to be equal to or less than the lower limit, it becomes easy to correct lateral chromatic aberration occurring in the entire zoom range, particularly in the peripheral portion of the imaging region. By not allowing the value of Conditional Expression (5) to be equal to or greater than the upper limit, it becomes easy to select a material having a relatively high refractive index as the material of the second negative lens from the object side, and as a result, it becomes easy to suppress distortion and field curvature.

Next, numerical examples of a zoom lens 30 will be described. Table 9 shows basic lens data of the zoom lens 30, Table 10 shows specification and variable surface distances during zooming, and Table 11 shows aspheric surface coefficients.

In Table 9, the column of Si shows a surface number i (i=1, 2, 3, . . . ) attached to an i-th surface of the elements, where i sequentially increases toward the image side in a case where an object side surface of an element closest to the object side is regarded as a first surface. The column of Ri shows a curvature radius of the i-th surface. The column of Di shows a surface distance on the optical axis Z between the i-th surface and an i+l-th surface. In Table 9, the column of Ndj shows a refractive index of a j-th (j=1, 2, 3, . . . ) element at the d line (a wavelength of 587.6 nm), where j sequentially increases toward the image side in a case where the element closest to the object side is regarded as the first element. The column of νdj shows an Abbe number of the j-th element based on a d line.

Here, reference signs of radii of curvature of surface shapes convex toward the object side are set to be positive, and reference signs of radii of curvature of surface shapes convex toward the image side are set to be negative. Table 9 additionally shows the aperture stop St and the optical members P1 to P3. In Table 9, in a place of a surface number of a surface corresponding to the aperture stop St, the surface number and a term of (St) are noted. A value at the bottom place of Di indicates a distance between the image plane Sim and the surface closest to the image side in the table. In Table 9, the variable surface distances, which are variable during zooming, are referenced by the reference signs DD[ ], and are written into places of Di, where object side surface numbers of distances are noted in [ ]. Further, in Table 9, regarding the variable surface distances, which change during focusing, the term (INF) and surface distances in a state where the object at infinity is in focus are noted.

In Table 10, values of the zoom ratio Zr, the focal length f of the whole system, the back focal length Bf in terms of the air conversion distance, the F number FNo., the maximum total angle of view 2ω, and the variable surface distance are shown based on the d line. (°) in the place of 2ω indicates that the unit thereof is a degree. In Table 10, values in the wide angle end state are shown in the column labeled by WIDE, and values in the telephoto end state are shown in the column labeled by TELE. The values in Tables 9 and 10 are values in a state where the object at infinity is in focus.

In Table 9, the reference sign * is attached to surface numbers of aspheric surfaces, and numerical values of the paraxial radius of curvature are written into the column of the radius of curvature of the aspheric surface. Table 11 shows aspheric surface coefficients of the aspheric surfaces. The “E−n” (n: an integer) in numerical values of the aspheric surface coefficients of Table 11 indicates “×10^(−n)”. The aspheric surface coefficients are values of the coefficients KA and Am (m=4, 6, 8, . . . ) in aspheric surface expression represented as the following expression.

${Zd} = {\frac{C \times h^{2}}{1 + \sqrt{1 - {{KA} \times C^{2} \times h^{2}}}} + {\sum\limits_{m}{{Am} \times h^{m}}}}$

-   -   here,     -   Zd: aspheric surface depth (a length of a perpendicular drawn         from a point on an aspheric surface at height h to a plane that         is perpendicular to the optical axis that contacts the vertex of         the aspheric surface)     -   h: a height (a distance from the optical axis to the lens         surface)     -   C: reciprocal of paraxial curvature radius     -   KA and Am: aspheric surface coefficients

In data of each table, a degree is used as a unit of an angle, and mm is used as a unit of a length, but since the optical system can be used with magnification and reduction in proportion, appropriate different units may be used. Further, each of the following tables shows numerical values rounded off to predetermined decimal places.

TABLE 9 Si Ri Di Ndj νdj  *1 641.66259  3.000 1.80100 34.97  2 33.75559 17.000  *3 123.74146  2.000 1.49700 81.54  4 56.40159 16.000  5 −72.32584  1.930 1.95375 32.32  6 −202.10991  0.300  7 136.61972  6.580 1.84666 23.78  8 −277.46991  0.75(INF)  9 −2306.32677  6.350 1.53775 74.70  10 −94.09392  6.161(INF)  11 114.6)313  7.660 1.43875 94.66 *12 −181.77945  4.121  13 −77.04720  1.800 1.80100 34.97  14 −126.53361  0.120  15 184.93960  1.800 1.95375 32.32  16 64.49500 16.610 1.43875 94.66  17 −57.48031  0.120  18 266.75570  7.670 1.43387 95.18  19 −90.09519  0.120  20 54.93968  4.520 1.72916 54.68  21 95.88929 DD[21]  22 39.58867  0.800 2.00100 29.13  23 15.50502  4.869  24 −33.46164  0.800 1.91082 35.25  25 81.63500  5.020 1.80518 25.42  26 −15.76600  0.810 1.77250 49.60  27 73.45119  0.120  28 34.32104  5.740 1.69895 30.13  29 −17.41600  0.800 1.95375 32.32  30 −74.84673 DD[30]  31 −33.54980  0.810 1.72916 54.68  32 59.17000  2.390 1.84661 23.88  33 −1406.19640 DD[33]  34(St) ∞  1.000 *35 64.73762  5.710 1.80610 40.88  36 −72.62275  0.120  37 131.85587  5.180 1.51742 52.43  38 −44.21500  1.000 1.95375 32.32  39 −230.81910 34.525  40 251.98617  3.390 1.84661 23.88  41 −68.85375  1.398  42 41.85229  6.010 1.58913 61.13  43 −51.64100  1.000 1.95375 32.32  44 26.58227  1.645  45 30.92090  9.460 1.53775 74.70  46 −26.31100  1.000 1.95375 32.32  47 −89.90422  0.120  48 69.93761  5.690 1.48749 70.24  49 −35.79182  0.200  50 ∞  1.000 1.51633 64.14  51 ∞  5.419  52 ∞ 33.000 1.60859 46.44  53 ∞ 13.200 1.51633 64.05  54 ∞  5.503

TABLE 10 WIDE TELE Zr 1.0 12.6 f 4.668 58.586 Bf 41.002 41.002 FNo. 1.86 2.67 2ω(°) 105.2 10.8 DD[21] 0.726 47.183 DD[30] 44.474 5.772 DD[33] 9.480 1.725

TABLE 11 Surface Number 1 3 12 35 KA   1.0000000E+00   1.0000000E+00   1.0000000E+00   1.0000000E+00 A4   2.1935986E−06 −4.8514385E−07   1.2227839E−06 −2.8441059E−06 A6 −5.0602429E−10 −8.4353254E−11 −9.0152102E−11 −6.5929982E−11 A8   9.2543372E−14 −1.8537680E−12 −3.6643047E−13   2.5648563E−11 A10 −2.1340794E−17   2.7757879E−15   1.2047269E−15 −3.2693830E−13 A12   1.3094908E−20 −5.6973394E−18 −4.2351771E−18   2.5112072E−15 A14 −8.8381246E−25   1.1850385E−20   9.0596803E−21 −1.1779118E−17 A16 −2.7337631E−27 −1.3306500E−23 −1.1002102E−23   3.2475601E−20 A18   1.2809320E−30   7.2223093E−27   7.0253554E−27 −4.8092328E−23 A20 −1.8339686E−34 −1.5476582E−30 −1.8330673E−30   2.9425260E−26

Here, it is preferable that the first lens group G1 and the fourth lens group G4, which are stationary lens groups, include at least one aspheric lens, and the aspheric lens is the lens 1 shown in FIGS. 1 and 2. At the telephoto end, the on-axis rays B0 t is relatively thick in the first lens group G1 and the fourth lens group G4 and the aspheric lens composed of the lens 1 is included in the first lens group G1 and/or the fourth lens group G4, which makes it possible to effectively reduce the blurriness of the ring zone at telephoto end. In the lens data of Table 9, the lens LA1 of the first lens group G1 having an aspheric optical surface indicated by surface number 1, the lens LA2 of the first lens group G1 having an aspheric optical surface indicated by surface number 3, the lens LC1 of the first lens group G1 having an aspheric optical surface indicated by surface number 12, and the lens of the fourth lens group G4 having an aspheric optical surface indicated by surface number 35 are composed of the lens 1.

FIGS. 16 and 17 show another example of the zoom lens comprising the lens 1.

FIG. 16 shows the state in which the focal length is at the wide angle end, and FIG. 17 shows the state in which the focal length is at the telephoto end. In FIGS. 16 and 17, the left side is the object side and the right side is the image side. Further, in FIG. 16, an arrow indicating a movement locus of each lens group during zooming from the wide angle end to the telephoto end, a point at which the imaging magnification is −1 (in the figure, horizontal dotted line indicated by β=−1), the on-axis rays wa and the rays wb at the maximum angle of view are shown together.

The zoom lens 40 substantially consists of, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power, a fourth lens group G4 having a positive refractive power, an aperture stop St, and a fifth lens group G5 having a positive refractive power. During zooming, the first lens group G1 is stationary with respect to the image plane Sim. During zooming from the wide angle end to the telephoto end, the distance between the first lens group G1 and the second lens group G2 is always widened, the distance between the second lens group G2 and the third lens group G3 is always narrowed, and the distance between the third lens group G3 and the fourth lens group G4 is narrower at the telephoto end than at the wide angle end. It should be noted that the aperture stop St shown in FIGS. 15 and 16 does not necessarily represent the size and the shape thereof, and indicates a position of the aperture stop on the optical axis Z.

In a case of applying the zoom lens 40 to an imaging apparatus, it is preferable to dispose a cover glass, a prism, and/or various filters such as an infrared cut filter and a low pass filter, between the optical system and the image plane Sim according to the configuration of the camera on which the lens is mounted. Therefore, FIGS. 16 and 17 show an example in which parallel flat plate-like optical members PP1 and PP2 assumed as the above members are disposed between the lens system and the image plane Sim.

With such a configuration, since the third lens group G3 and the fourth lens group G4 correct the fluctuation in the position of the image plane caused by zooming of the second lens group G2 that operates on zooming and move relative to each other, it is possible to correct field curvature of the image plane during zooming and possible to favorably correct fluctuation in the spherical aberration during zooming.

In addition, with the configuration in which movement is performed such that the distance between the third lens group G3 and the fourth lens group G4 is narrower on the telephoto side than on the wide angle side, the movement range of the second lens group G2 on the telephoto side can be made wide and the refractive power of the second lens group G2 can be suppressed. In this way, it is possible to suppress aberration fluctuation accompanied by zooming.

In addition, the second lens group G2 substantially consists of, in order from the object side, a first lens component, a second lens component, a third lens component, and a fourth lens component. The first lens component is a second a negative lens L2 a with the concave surface facing toward the image side, the absolute value of the curvature radius of the surface being smaller than that of the surface on the object side. The second lens component is a cemented lens in which a second bn biconcave lens L2 bn and a second bp positive meniscus lens L2 bp are cemented in order from the object side and which has a negative refractive power as a whole. The third lens component is a cemented lens in which a second cn biconcave lens L2 cn and a second cp positive lens L2 cp are cemented in order from the object side. The fourth lens component is a second d negative lens L2 d with a concave surface facing toward the object side, the absolute value of the curvature radius of the surface being smaller than that of the surface on the image side.

Since, in a case where the second lens group G2 has more than four lens components, the moving range of the second lens group G2 becomes difficult to be obtained, and in a case where the second lens group G2 has less than four lens components, suppression of various aberrations becomes difficult, the second lens group G2 is composed of four lens components. In this way, it is possible to achieve both the securing of the moving range of the second lens group G2 and the suppressing of various aberrations.

Further, in order to achieve high magnification, the principal point position of the second lens group G2 needs to be closer to the object side, so it is necessary to increase the number of negative lenses in the second lens group G2.

By composing the first lens component as described above, it is possible to suppress occurrence of distortion and astigmatism on the wide angle side.

By arranging a negative lens on the image side of the second lens component, it is possible to make the principal point position close to the object side. However, since lateral chromatic aberration tends to occur on the wide angle side, the second lens component is set to be a cemented lens in which the second bn biconcave lens L2 bn and the second bp positive meniscus lens L2 bp are cemented as described above and have a negative refractive power as a whole, which makes possible to correct the lateral chromatic aberration while making the principal point position close to the object side. Further, by making the image side of the second bp positive meniscus lens L2 bp concave, there is an advantage in achieving the wide angle.

Since the image side of the second lens component is concave, it is possible to suppress occurrence of spherical aberration on the telephoto side by setting a lens concave toward the object side to be arranged closest to the object side, with respect to the third lens component. Further, by using a cemented lens of the second cn biconcave lens L2 cn and the second cp positive lens L2 cp, it is possible to correct longitudinal chromatic aberration on the telephoto side.

Since the object side of the fourth lens component is concave, the fourth lens component works for correcting astigmatism generated by the first lens group G1 on the wide angle side while suppressing occurrence of spherical aberration on the telephoto side. In addition, since the fourth lens component is a negative lens, the fourth lens component works for strengthening a negative refractive power of the whole second lens group G2.

In the zoom lens, it is preferable that the fifth lens group G5 remains stationary with respect to the image plane Sim during zooming, and a third-fourth composite lens group formed by joining the third lens group G3 and the fourth lens group G4 and the second lens group G2 simultaneously pass through a point at which respective imaging magnifications are −1 during zooming from the wide angle end to the telephoto end. With such a configuration, it is possible to increase the zoom ratio without the third lens group G3 returning to the image side during zooming from the wide angle end to the telephoto end.

Next, numerical examples of a zoom lens 40 will be described. Table 12 shows basic lens data of the zoom lens 40, Table 13 shows data on specification, Table 14 shows data on the surface distance in which the distance changes during zooming, and Table 15 shows data on aspheric surface coefficients.

In the lens data of Table 12, the column of the surface number shows a surface number that sequentially increases toward the image side, with the surface of an element closest to the object side being regarded as the first surface. The column of the curvature radius shows curvature radii of the respective surfaces. The column of the surface distance shows surface distances on the optical axis Z between the respective surfaces and the next surfaces. The column of nd shows the refractive indexes of respective optical elements at the d line (a wavelength of 587.6 nm), and the column of νd shows Abbe numbers of respective optical elements at the d line (a wavelength of 587.6 nm), and the column of θgF shows the partial dispersion ratios of respective optical elements.

The partial dispersion ratio θgF is expressed by the following expression.

θgF=(ng−nF)/(nF−nC)

-   -   here,     -   ng: refractive index at the g line     -   nF: refractive index at the F line     -   nC: refractive index at the C line

Here, reference signs of curvature radii are set to be positive in a case where the surface shapes are convex toward the object side, and reference signs of curvature radii are set to be negative in a case where the surface shapes are convex toward the image side. The basic lens data includes an aperture stop St and optical members PP1 and PP2. In the place of a surface number of a surface corresponding to the aperture stop St, the surface number and a term of (stop) are noted. Further, in the lens data of Table 12, DD [surface number] is described in the place of the surface distance in which the distance changes during zooming. The numerical values corresponding to DD [surface number] are shown in Table 14.

Values of a zoom magnification, a focal length f′, an F value FNo., and a total angle of view 2ω are shown in data on the specification in Table 13.

In the basic lens data, the data on specification, and the data on changing surface distance, a degree is used as a unit of an angle, and mm is used as a unit of a length, but since the optical system can be used with magnification and reduction in proportion, appropriate different units may be used.

In the lens data of Table 12, the reference sign * is attached to surface numbers of aspheric surfaces, and numerical values of the paraxial curvature radii are shown as the curvature radius of the aspheric surface. The data on the aspheric surface coefficients in Table 15 show surface numbers for the aspheric surfaces and the aspheric surface coefficients for the aspheric surfaces. The “E±n” (n: an integer) in numerical values of the aspheric surface coefficients indicates “×10^(±n)”. The aspheric surface coefficients are values of the coefficients KA and Am (m=3 . . . 16) in aspheric expression represented as the following expression.

Zd=C·h ²/{1+(1−KA·C ² ·h ²)^(1/2) }+ΣAm·h ^(m)

-   -   here,     -   Zd: aspheric surface depth (a length of a perpendicular drawn         from a point on an aspheric surface at height h to a plane that         is perpendicular to the optical axis that contacts the vertex of         the aspheric surface)     -   h: height (a distance from the optical axis)     -   C: reciprocal of paraxial curvature radius     -   KA, Am: aspheric surface coefficient (m=3 . . . 16)

TABLE 12 Surface Curvature Surface Number Radius Distance nd νd θgF  1 −13378.35006 5.977 1.77250 49.60 0.55212  2 506.33763 16.475  3 −584.49773 4.800 1.80400 46.58 0.55730  4 335.43813 2.500  5 349.09925 12.000 1.84139 24.56 0.61274  6 8435.34081 4.877  7 7849.07545 5.000 1.80000 29.84 0.60178  8 439.82608 18.270 1.49700 81.54 0.53748  9 −444.99046 0.125  10 1000.00000 10.877 1.63246 63.77 0.54215  11 −1249.86489 34.999  12 336.67292 23.000 1.43387 95.18 0.53733  13 −555.44540 1.838  14 224.29284 6.264 1.63980 34.47 0.59233  15 143.35462 28.031 1.43875 94.94 0.53433  16 8626.60879 3.144  17 176.57760 17.500 1.49700 81.54 0.53748  18 475.02631 DD[18]  19 182.61414 4.500 1.95375 32.32 0.59015  20 86.38802 12.791  21 −331.30207 3.073 1.55032 75.50 0.54001  22 61.69495 4.501 1.54814 45.78 0.56859  23 78.10163 9.831  24 −145.36707 2.145 1.49700 81.54 0.53748  25 96.62937 7.000 1.84139 24.56 0.61274  26 −687.33596 5.926  27 −76.16819 2.130 1.43875 94.94 0.53433  28 1644.59414 DD[28]  29 4104.02749 7.091 1.43875 94.66 0.53402  30 −137.72084 0.177  31 2020.97885 7.824 1.43875 94.66 0.53402  32 −125.76283 2.257 1.94692 32.77 0.58862  33 −185.59421 DD[33]  34 124.45199 6.891 1.80390 32.49 0.59305  35 90.80287 10.021 1.43875 94.66 0.53402  36 −49972.97817 2.118  37 817.29840 6.060 1.43875 94.66 0.53402 *38 −343.72331 DD[38]  39 (stop) ∞ 7.705  40 −170.68031 4.420 1.51793 61.26 0.54257  41 1424.66641 1.393  42 854.58215 4.351 1.84139 24.56 0.61274  43 −298.35856 3.656 1.83481 42.72 0.56486  44 408.16101 22.581  45 −124.70799 2.963 1.63723 35.15 0.58660  46 545.65832 5.104 1.84139 24.56 0.61274  47 −188.00072 0.570  48 59.62634 5.814 1.73532 53.96 0.54449  49 1199.51213 3.520 1.72395 29.02 0.60094  50 86.05183 19.251  51 144.47442 7.880 1.74356 40.77 0.57416  52 −63.44339 2.500 1.92486 36.38 0.57719  53 99.00655 14.855  54 342.36858 5.042 1.84139 24.56 0.61274  55 −97.66651 13.086  56 222.75255 4.531 1.52189 50.90 0.55751  57 21.13645 6.601 1.49700 81.54 0.53748  58 48.14182 8.035  59 95.08701 6.958 1.49700 81.54 0.53748  60 −37.48307 2.876 1.95375 32.32 0.59015  61 −260.67641 9.976  62 55.91542 4.808 1.53515 57.90 0.54800  63 −387.96848 2.000  64 ∞ 1.500 1.51633 64.14 0.53531  65 ∞ 0.000  66 ∞ 3.690 1.51633 64.14 0.53531  67 ∞ 35.589

TABLE 13 Wide Angle Telephoto End Intermediate End Zoom 1.0 3.8 19.8 Magnification F′ 34.993 134.373 692.862 FNo. 2.85 2.85 4.85 2ω[°] 44.8 11.8 2.4

TABLE 14 Wide Angle Telephoto End Intermediate End DD[18] 5.430 85.787 118.419 DD[28] 231.414 131.867 2.255 DD[33] 24.452 5.861 2.307 DD[38] 2.654 40.435 140.970

TABLE 15 Surface Number 38 KA −6.0660447E+00 A3   0.0000000E+00 A4 −2.8516819E−09 A5 −3.7645381E−10 A6   5.1922095E−11 A7 −1.9515833E−13 A8   4.9687016E−14 A9 −1.0574536E−14 A10   2.5263117E−17 A11   2.5847685E−17 A12 −7.1492956E−19 A13   3.0977491E−21 A14 −1.5830950E−22 A15   9.3185221E−24 A16 −1.0801038E−25

Here, it is preferable that the third lens group G3 and the fourth lens group G4, which are moving lens groups, include at least one aspheric lens, and the aspheric lens is the lens 1 shown in FIGS. 1 and 2. The on-axis rays wa is relatively thick in the third lens group G3 and the fourth lens group G4 and the aspheric lens composed of the lens 1 is included in the third lens group G3 and/or the fourth lens group G4, which makes it possible to effectively reduce the blurriness of the ring zone in any zoom range from the wide angle end to the telephoto end. In the lens data of Table 12, the lens L4 c of the fourth lens group G4 having aspheric optical surfaces indicated by the surface number 38 is composed of the lens 1.

FIG. 18 shows an example of an imaging lens comprising the lens of FIG. 1.

In FIG. 18, the left side is the object side and the right side is the image side.

The imaging lens 50 shown in FIG. 18 is substantially composed of, in order from the object side along the optical axis Z, the first lens group G1 that has a positive refractive power, the stop St, and the second lens group G2 that has a positive refractive power.

In a case of applying the imaging lens 50 to an imaging apparatus, it is preferable to dispose a cover glass, a prism, and various filters such as an infrared cut filter and a low pass filter between the optical system and the image plane Sim according to the configuration of the camera on which the lens is mounted. Therefore, FIG. 18 shows an example in which parallel flat plate-like optical members PP assumed as the above member are disposed between the lens system and the image plane Sim.

The first lens group G1 is composed to include, in order from the object side, two continuous positive lenses and a negative lens L15 having concave surface facing toward the image side.

The second lens group G2 is composed to include, in order from the object side, a lens L21 having at least one aspheric surface, and a three-piece cemented lens in which a positive lens L22 convex toward the image side, a negative lens L23, and a positive lens L24 are cemented in order from the object side, and the three-piece cemented lens has a positive refractive power.

As described above, in the lens system consisting of, in order from the object side, the first lens group G1 having a positive refractive power, the stop St, and the second lens group G2 having a positive refractive power, since the lens compositions of the first lens group G1 and the second lens group G2 are suitably set, it is possible to set the imaging lens to have a high optical performance, where the total length is short, the aperture is large, and various aberrations, including spherical aberration and chromatic aberration, are favorably corrected.

Further, by arranging a Gaussian type composed of two continuous positive lenses and a negative lens L15 having concave surface facing toward the image side on the object side of the stop St, spherical aberration is favorably corrected, and by arranging the aspheric lens L21 and the three-piece cemented lens (L22 to L24) on the image side of the stop St, spherical aberration, longitudinal chromatic aberration, and lateral chromatic aberration are favorably corrected.

By arranging the aspheric lens L21 in the vicinity of the image side of the stop St, the spherical aberration can be corrected without making a strong concave surface, which makes it possible to prevent the back focus from extending.

Further, since the cemented lens is composed of the positive lens L22, the negative lens L23, and the positive lens L24, it is possible to achieve good correction without causing total reflection of rays between the respective lenses. In addition, in the three-piece cemented lens, two positive lenses are arranged at both ends in order to have a positive refractive power, and thus respective aberrations can be assigned to two positive lenses.

In the imaging lens 50, in focus adjustment from an object at infinity to a close-range object, it is preferable that the first lens group G1 remains stationary with respect to the image plane. In this way, focusing is performed only by the whole or a part of the second lens group G2, and the weight of the moving lens can be reduced as compared with the case where focusing is performed also including the first lens group G1. Therefore, an improvement in focus speed can be expected.

Next, numerical examples of the imaging lens 50 will be described. Table 16 shows basic lens data of the imaging lens 50, Table 17 shows data on specification, and Table 18 shows data on aspheric surface coefficients.

In the lens data of Table 16, the column of the surface number shows a surface number that sequentially increases toward the image side, with the surface of an element closest to the object side being regarded as the first surface. The column of the curvature radius shows curvature radii of the respective surfaces. The column of the distance shows distances on the optical axis Z between the respective surfaces and the next surfaces. The column of nd shows the refractive indexes of respective optical elements at a d line (a wavelength of 587.6 nm), and the column of νd shows Abbe numbers of respective optical elements at the d line (a wavelength of 587.6 nm), and the column of θgF shows the partial dispersion ratios of respective optical elements.

Reference signs of curvature radii are set to be positive in a case where the surface shapes are convex toward the object side, and reference signs of curvature radii are set to be negative in a case where of the surface shapes are convex toward the image side. The basic lens data also includes the stop St. In the column of a surface number of a surface corresponding to the stop St, the surface number and a term of (stop) are noted.

Values of a focal length f, a back focus BF, a total angle of view 2ω, and an F value FNo. are shown in data on the specification in Table 17.

In the lens data of Table 16, the reference sign * is attached to surface numbers of aspheric surfaces, and numerical values of the paraxial curvature radii are shown as the curvature radius of the aspheric surface. The data on the aspheric surface coefficients in Table 18 show surface numbers for the aspheric surfaces and the aspheric surface coefficients for the aspheric surfaces. The aspheric surface coefficients are values of the coefficients K and Am (m=3, 4, 5 . . . 20) in aspheric surface expression represented as the following expression.

Zd=C·h ²/{1+K·C ² ·h ²)^(1/2) }+ΣAm·h ^(m)

-   -   here,     -   Zd: aspheric surface depth (a length of a perpendicular drawn         from a point on an aspheric surface at height h to a plane that         is perpendicular to the optical axis that contacts the vertex of         the aspheric surface)     -   h: height (a distance from the optical axis)     -   C: reciprocal of paraxial curvature radius     -   K and Am: aspheric surface coefficients (m=3, 4, 5 . . . , 20).

In basic lens data and expression data, a degree is used as a unit of an angle, and mm is used as a unit of a length, but since the optical system can be used with magnification and reduction in proportion, appropriate different units may be used.

TABLE 16 Surface Curvature Number Radius Distance nd νd θgF  1 118.040 2.45 1.69680 55.5  2 226.170 0.15  3 39.651 6.20 1.49700 81.6  4 122.610 0.15  5 33.611 5.10 1.49700 81.6 0.5375  6 66.540 0.15  7 24.239 9.93 1.49700 81.6  8 33.111 0.75  9 40.570 1.19 1.68893 31.2  10 14.632 5.82 ∞ 9.80 *12 −25.211 4.15 1.80610 40.9 *13 −39.046 0.21  14 155.760 6.71 1.88300 40.8  15 −16.669 1.08 1.64769 33.8  16 23.016 6.43 1.88300 40.8  17 130.660 0.84  18 83.297 2.12 2.00069 25.5  19 248.430 10.00  20 ∞ 2.80 1.51680 64.2  21 ∞

TABLE 17 f 56.74 BF 14.15 2ω 28.2 Fno 1.25

TABLE 18 Surface Number 12 13 K   0.0000000E+00   0.0000000E+00 A3 −5.4390191E−06   2.0197209E−05 A4   7.6906609E−06   4.6316479E−06 A5 −1.9892955E−06   1.2763791E−06 A6   1.3009389E−07 −1.0982860E−07 A7   2.1383723E−09 −9.4499747E−10 A8 −3.5100915E−10   3.6819654E−10 A9 −2.3107027E−11   2.2509649E−11 A10 −3.4335228E−13   2.7190007E−13 A11   5.0905398E−14 −5.8050703E−14 A12   5.4740741E−15 −6.2170865E−15 A13   3.1623233E−16 −3.8573259E−16 A14   9.8821792E−18 −1.6015358E−17 A15 −2.9640085E−19 −2.0425376E−19 A16 −8.1938746E−20   4.2635187E−20 A17 −8.9348387E−21   5.9320562E−21 A18 −7.6842542E−22   5.4278679E−22 A19 −5.8823241E−23   4.2137980E−23 A20 −4.2010122E−24   2.9861951E−24

Here, it is preferable that the second lens group G2 includes at least one aspheric lens, and the aspheric lens is the lens 1 shown in FIGS. 1 and 2. In the second lens group G2, it is possible to reduce the fluctuation in the shape of the blurriness of the ring zone during focusing. In the lens data of Table 16, the lens L21 of the second lens group G2 having aspheric optical surfaces indicated by the surface number 12 and the surface number 13 is composed of the lens 1.

As described above, the lens disclosed in the present specification has random unevenness within an optical effective diameter of an optical surface, in which an arithmetic mean roughness within the optical effective diameter of the optical surface is 20 nm or more and 50 nm or less, and an average value of widths of protrusion portions of the unevenness on an average line of a roughness curve of the optical surface is 1/200 or more and 1/50 or less of the optical effective diameter of the optical surface.

Further, the standard deviation of the widths of the protrusion portions is less than 1/125 of the optical effective diameter of the optical surface.

Furthermore, the arithmetic mean roughness within the optical effective diameter of the optical surface is 20 nm or more and 30 nm or less, and an average value of widths of protrusion portions of the unevenness on an average line of a roughness curve of the optical surface is 1/100 or more and 1/50 or less of the optical effective diameter of the optical surface.

In addition, the optical surface is aspheric.

The zoom lens disclosed in the present specification consists of, in order from an object side, a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming, a plurality of moving lens groups that move independently of each other during zooming, and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, in which the moving lens group includes at least one aspheric lens, and the aspheric lens is the lens.

The zoom lens disclosed in the present specification consists of, in order from an object side, a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming, a plurality of moving lens groups that move independently of each other during zooming, and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, in which one or both of the first stationary lens group and the second stationary lens group includes at least one aspheric lens, and the aspheric lens is the lens.

Furthermore, the imaging lens disclosed in the present specification consists of, in order from an object side, a first lens group, a stop, and a second lens group having a positive refractive power, the first lens group being stationary with respect to an image plane during focus adjustment from an object at infinity to a close-range object, in which the second lens group includes at least one aspheric lens, and the aspheric lens is the lens.

EXPLANATION OF REFERENCES

-   -   1: lens     -   2: optical surface     -   3: protrusion portion     -   C1: roughness curve     -   C2: average line     -   D: optical effective diameter     -   W: width of protrusion portion     -   10: zoom lens     -   G1: first lens group     -   G2: second lens group     -   G3: third lens group     -   G4: fourth lens group     -   G5: fifth lens group     -   L1 a to L1 j: lens     -   L2 a: lens     -   L3 a to L3 e: lens     -   L4 a, L4 b: lens     -   L5 a to L51: lens     -   PP1, PP2: optical member     -   St: aperture stop     -   Sim: image plane     -   wa: on-axis rays     -   wb: rays at maximum angle of view     -   Z: optical axis     -   20: zoom lens     -   G1: first lens group     -   G2: second lens group     -   G3: third lens group     -   G4: fourth lens group     -   G5: fifth lens group     -   L11 to L15: lens     -   L21 to L26: lens     -   L31: lens     -   L41 to L45: lens     -   L51 to L62: lens     -   PP1 to PP3: optical member     -   St: aperture stop     -   Sim: image plane     -   wa: on-axis rays     -   wb: rays at maximum angle of view     -   Z: optical axis     -   30: zoom lens     -   B0 w, B0 t: on-axis rays     -   B1 w, B1 t: off-axis rays at maximum angle of view     -   G1: first lens group     -   G1A: front group of the first lens group     -   G1B: intermediate group of the first lens group     -   G1C: rear group of the first lens group     -   G2: second lens group     -   G3: third lens group     -   G4: fourth lens group     -   G4A: front group of the fourth lens group     -   G4B: rear group of the fourth lens group     -   G5: fifth lens group     -   LA1 to LA4: lens     -   LB1: lens     -   LC1 to LC6: lens     -   P1 to P3: optical member     -   St: aperture stop     -   Sim: image plane     -   Z: optical axis     -   40: zoom lens     -   G1: first lens group     -   G1 a: front group of the first lens group     -   G1 b: intermediate group of the first lens group     -   G1 c: rear group of the first lens group     -   G2: second lens group     -   G3: third lens group     -   G4: fourth lens group     -   G5: fifth lens group     -   L1 a to L1 j: lens     -   L2 a to L2 d: lens     -   L3 a to L3 c: lens     -   L4 a to L4 c: lens     -   L5 a to L5 o: lens     -   PP1, PP2: optical member     -   St: aperture stop     -   Sim: image plane     -   wa: on-axis rays     -   wb: rays at maximum angle of view     -   Z: optical axis     -   50: imaging lens     -   G1: first lens group     -   G2: second lens group     -   L11 to L15: lens     -   L21 to L25: lens     -   PP: optical member     -   St: stop     -   Sim: image plane     -   Z: optical axis 

What is claimed is:
 1. A lens, comprising: unevenness within an optical effective diameter of an optical surface, wherein an arithmetic mean roughness within the optical effective diameter of the optical surface is 20 nm or more and 50 nm or less, and an average value of widths of protrusion portions of the unevenness on an average line of a roughness curve of the optical surface is 1/200 or more and 1/50 or less of the optical effective diameter of the optical surface.
 2. The lens according to claim 1, wherein a standard deviation of the widths of the protrusion portions is less than 1/125 of the optical effective diameter of the optical surface.
 3. The lens according to claim 1, wherein the arithmetic mean roughness within the optical effective diameter of the optical surface is 20 nm or more and 30 nm or less, and the average value of the widths of the protrusion portions of the unevenness on the average line of the roughness curve of the optical surface is 1/100 or more and 1/50 or less of the optical effective diameter of the optical surface.
 4. The lens according to claim 2, wherein the arithmetic mean roughness within the optical effective diameter of the optical surface is 20 nm or more and 30 nm or less, and the average value of the widths of the protrusion portions of the unevenness on the average line of the roughness curve of the optical surface is 1/100 or more and 1/50 or less of the optical effective diameter of the optical surface.
 5. The lens according to claim 1, wherein the optical surface is aspheric.
 6. The lens according to claim 2, wherein the optical surface is aspheric.
 7. The lens according to claim 3, wherein the optical surface is aspheric.
 8. The lens according to claim 4, wherein the optical surface is aspheric.
 9. A zoom lens consisting of, in order from an object side: a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming; a plurality of moving lens groups that move independently of each other during zooming; and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, wherein the moving lens group includes at least one aspheric lens, and the aspheric lens is the lens according to claim
 5. 10. A zoom lens consisting of, in order from an object side: a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming; a plurality of moving lens groups that move independently of each other during zooming; and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, wherein the moving lens group includes at least one aspheric lens, and the aspheric lens is the lens according to claim
 6. 11. The zoom lens according to claim 9, wherein the moving lens group includes in order from the object side, a negative moving lens group having a negative refractive power, a first positive lens group having a positive refractive power, and a second positive lens group having the positive refractive power.
 12. The zoom lens according to claim 11, wherein the first positive lens group or the second positive lens group includes the aspheric lens.
 13. A zoom lens consisting of, in order from an object side: a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming; a plurality of moving lens groups that move independently of each other during zooming; and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, wherein one or both of the first stationary lens group and the second stationary lens group include at least one aspheric lens, and the aspheric lens is the lens according to claim
 5. 14. A zoom lens consisting of, in order from an object side: a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming; a plurality of moving lens groups that move independently of each other during zooming; and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, wherein one or both of the first stationary lens group and the second stationary lens group include at least one aspheric lens, and the aspheric lens is the lens according to claim
 6. 15. A zoom lens consisting of, in order from an object side: a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming; a plurality of moving lens groups that move independently of each other during zooming; and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, wherein one or both of the first stationary lens group and the second stationary lens group include at least one aspheric lens, and the aspheric lens is the lens according to claim
 7. 16. A zoom lens consisting of, in order from an object side: a first stationary lens group that has a positive refractive power and is stationary with respect to an image plane during zooming; a plurality of moving lens groups that move independently of each other during zooming; and a second stationary lens group that is positioned closest to an image side, has a positive refractive power, and is stationary with respect to the image plane during zooming, wherein one or both of the first stationary lens group and the second stationary lens group include at least one aspheric lens, and the aspheric lens is the lens according to claim
 8. 17. An imaging lens, consisting of, in order from an object side: a first lens group; a stop; and a second lens group having a positive refractive power, wherein the first lens group is stationary with respect to an image plane during focus adjustment from an object at infinity to a close-range object, and the second lens group includes at least one aspheric lens, and the aspheric lens is the lens according to claim
 5. 18. An imaging lens, consisting of, in order from an object side: a first lens group; a stop; and a second lens group having a positive refractive power, wherein the first lens group is stationary with respect to an image plane during focus adjustment from an object at infinity to a close-range object, and the second lens group includes at least one aspheric lens, and the aspheric lens is the lens according to claim
 6. 19. An imaging lens, consisting of, in order from an object side: a first lens group; a stop; and a second lens group having a positive refractive power, wherein the first lens group is stationary with respect to an image plane during focus adjustment from an object at infinity to a close-range object, and the second lens group includes at least one aspheric lens, and the aspheric lens is the lens according to claim
 7. 20. An imaging lens, consisting of, in order from an object side: a first lens group; a stop; and a second lens group having a positive refractive power, wherein the first lens group is stationary with respect to an image plane during focus adjustment from an object at infinity to a close-range object, and the second lens group includes at least one aspheric lens, and the aspheric lens is the lens according to claim
 8. 